Golf club head

ABSTRACT

A hollow golf club head has a head volume of not less than 430 cc, a lateral moment of inertia of from 5000 to 5900 g sq·cm, and a club head thickness of from 45 to 58 mm. 
     In a vertical plane including a sweet spot and the center of gravity of the head, preferably, a crown surface length measured along the upper outer surface of the club head from an upper edge of a club face to the rearmost point of the club head is set in a range of from 1.02 to 1.20 times a sole surface length measured along the lower outer surface of the club head from a lower edge of the club face to the rearmost point of the club head.

BACKGROUND OF THE INVENTION

The present invention relates to a golf club head capable of reducingthe variation in the carry distance of a struck ball and therebyincreasing the carry distances in totality.

The directional stability of a struck ball is an important factor forstabilizing the carry distance. If the ball is struck off-center, theclub head is moved or rotates around the center of gravity of the headmore or less. If such a rotational movement of the club head at the timeof off-center shot is reduced, then the lunching direction of the struckball is stabilized.

In recent years, on the other hand, large-sized various wood-type golfclub heads have been proposed. Usually, the large-sized golf club headsare increased in the lateral moment of inertia and vertical moment ofinertia.

If the vertical moment of inertia is increased, then the vertical geareffect becomes reduced, therefore, if the ball hitting position is offthe sweet spot upward or downward, the carry distance tends to decrease.

AS well known in the art, the vertical gear effect is as follows. If theball hitting position is off the sweet spot SS upwards or downwards,then as shown in FIG. 6, with respect to a horizontal axis extending inthe toe-heel direction passing through the center of gravity G of thehead, there is caused a moment which is a product of the impact force Freceived from the golf ball (b) and the distance L1 or L2 between thehitting position and the center of gravity G measured perpendicular tothe direction of the force F. As a result, the club head is rotatedaround the horizontal axis by a small angle.

Due to the frictional engagement between the golf ball and the club face(f), the contact surface of the golf ball receives a force in thereverse direction to the rotational direction of the club head like agear. As a result, the backspin of the struck ball is decreased in thecase of an upper hitting position or increased in the case of a lowerhitting position.

In consequence, in the case of the golf club heads whose vertical momentof inertia is large where the rotational movement is decreased asexplained above, if the ball hitting position is off the sweet spotupward, the backspin can not be fully decreased.

On the other hand, due to the face roll having a radius of curvature Y,in the case of the upper hitting position, when compared with the sweetspot SS, the loft angle becomes increased and the launch angle of thestruck ball is also increased. As a result, the ballistic course is veryliable to become a rising trajectory and thereby the carry distance isdecreased.

Contrary, in the case of the lower hitting position, the backspin cannot be fully increased, and the launch angle of the ball is decreased.As a result, the ball tends to drop quickly and thereby the carrydistance is decreased.

Thus, in the case of a large-sized golf club head, due to the relativelylarge vertical moment of inertia, there is a tendency that the carrydistance varies wide depending of the ball hitting position.

SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide a golfclub head in which, by increasing the lateral moment of inertia anddecreasing the thickness of the club head, the vertical moment ofinertia is decreased on the whole, and thereby the variation in thecarry distance can be reduced.

According to the present invention, a hollow golf club head has a headvolume of not less than 430 cc, a lateral moment of inertia of from 5000to 5900 g sq·cm, and a club head thickness of from 45 to 58 mm.

Therefore, the vertical moment of inertia is decreased. As a result,even if the ball hitting position is off the sweet spot upward ordownward, the struck ball benefits from the vertical gear effect and thedecrease in the carry distance is controlled.

Further, since the lateral moment of inertia is very large, even if theball hitting position is off the sweet spot toward the toe or heel, thelateral movement of the club head becomes very small, and thedirectional stability of the struck ball is improved, therefore, thedecrease in the carry distance is controlled.

DEFINITIONS

In this specification, sizes, positions, directions and the likerelating to the club head refer to those under a standard state of theclub head unless otherwise noted.

Here, the standard state of the club head 1 is such that the club headis set on a horizontal plane HP so that the center line CL of the clubshaft (not shown) is inclined at the lie angle (alpha) while keeping theclub shaft center line CL on a vertical plane VP1, and the club face 2forms its loft angle (beta) with respect to the horizontal plane HP.Incidentally, in the case of the club head alone, the center line of theshaft inserting hole (h) can be used instead of the center line of theclub shaft.

Lateral moment of inertia Ma is the moment of inertia around a verticalaxis A1 passing through the center of gravity G in the standard state.

Vertical moment of inertia Mb is the moment of inertia around ahorizontal axis A2 passing through the center of gravity G in theheel-and-toe direction of the head in the standard state.

Sweet spot SS is the point of intersection between the club face and astraight line N drawn normally to the club face 2 passing the center ofgravity G of the head.

Back-and-forth direction is a direction parallel with theabove-mentioned straight line N projected on the horizontal plane HP.

Heel-and-toe direction is a direction TH parallel with the horizontalplane HP and perpendicular to the back-and-forth direction.

Club head thickness H is the height measured from the horizontal planeHP to the highest point (m) on the crown portion of the club head,namely, the highest point of the head excluding the upwardly protrudinghosel portion if any.

Sweet spot height GH is a height of the sweet spot Ss measured from thehorizontal plane HP.

Face progression FP is the horizontal distance between the leading edgeLe of the club head and the vertical plane VP1 including the club shaftcenter line CL, measured in a vertical plane VP3 including the sweetspot SS and the center of gravity G.

Leading edge Le is a contact point between the club face 2 and avertical plane VP2 parallel with the vertical plane VP1.

Gravity point depth GL is the horizontal distance between the center ofgravity G and the vertical plane VP2.

Wood-type golf club is meant for at least number 1 to 5 woods, and clubscomprising heads having similar shapes may be included.

If the edge (2 a and 2 b) of the club face 2 is unclear due to smoothchange in the curvature, as shown in FIGS. 5( a) and 5(b), a virtualedge line (Pe) defined based on the curvature change is used instead asfollows. In each cutting plane E1, E2—including the sweet spot sS andthe center G of gravity of the head, a point Pe at which the radius (r)of curvature of the profile line Lf of the face portion first becomesunder 200 mm in the course from the center ss to the periphery of theclub face is determined. Then, the virtual edge line is defined as alocus of the points Pe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view a club head according to the present invention.

FIG. 2 is a top view of the club head.

FIG. 3 is a cross sectional view taken along a vertical plane (line A-Ain FIG. 2) including the sweet spot and the center of gravity of theclub head.

FIG. 4 is a heel-side side view of the club head.

FIG. 5( a) and FIG. 5( b) are a front view and a cross sectional view ofa face portion of a head for explaining the edge of the club face.

FIG. 6 is a cross sectional view for explaining a vertical gear effectof a club head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings, golf club head 1 according to the present invention isa wood-type hollow golf club head. The head 1 comprises a face portion 3whose front face defines a club face 2 for striking a ball; a crownportion 4 intersecting the club face 2 at the upper edge 2 a thereof; asole portion 5 intersecting the club face 2 at the lower edge 2 bthereof; a side portion 6 between the crown portion 4 and sole portion5; and a hosel portion 7 disposed at the heel-side end to be attached toan end of a club shaft inserted into a shaft inserting hole (h). Theclub head 1 is provided a shell structure with thin walls having aclosed hollow (i).

The club face 2 is provided with a face roll (a curvature from crown tosole) of a radius of curvature PR, and a face bulge (a curvature fromheel to toe) of a radius of curvature RB.

The outer surface of the crown portion 4 is convexly curved. Thus, apartfrom the hosel portion 7, the highest point (m) is positioned within theouter surface of the crown portion 4.

The hosel portion 7 has a tubular portion protruding upwardly from thecrown portion 4 and defining the shaft inserting hole (h).

The outer surface of the hosel portion 7 is connected to the outersurface of the crown portion 4 through a transitional concave curve.

The side portion 6 can be formed to extend continuously from the toe tothe heel through the rear of the head. But, in this embodiment, the sideportion 6 is formed discontinuously.

In this embodiment, the club head 1 is made of metal materials. But, inorder to reduce the club head weight and/or to adjust the position ofthe center of gravity G of the head, a fiber reinforced resin can beused together with the metal materials. Preferably used are metalmaterials having a large specific tensile strength, for example,stainless steels, maraging steels, pure titanium, titanium alloys,magnesium alloys aluminum alloys and the like are. In the case of thetitanium alloys, for example Ti-6Al-4V, Ti-15V-3Cr-3Al-3Sn,Ti-15Mo-5Zr-3Al, Ti-13V-11Cr-3Al and the like are be preferably used.

The club head 1 is manufactured by assembling a plurality of parts(usually 2 to 5 parts) each prepared by an appropriate method, forexample, casting, rolling, forging, pressure molding or the like.

The volume of the club head 1 is set in a range of not less than 430 cc,preferably not less than 440 cc, more preferably not less than 450 cc.

Such a large head volume can give the user easy feelings at the time ofaddressing the ball and can increase the gravity point depth GL and thelateral moment of inertia Ma so as to improve the directional stabilityof the struck ball.

If the volume is less than 430 cc, it becomes difficult to improve thedirectional stability of the struck ball.

If the volume is too large, on the other hand, problems arise such asincrease in the club head weight, deterioration of swing balance,decrease in the durability and the like, therefore, it is preferablethat the volume is set to be not more than 600 cc, preferably not morethan 550 cc. If golf rules are considered, the volume should be not morethan 460 cc.

If the mass of the club head 1 is too small, then the lateral moment ofinertia is decreased, and also the kinetic energy during swing isdecreased, therefore, the improvement in the carry distance can not beexpected. If the mass of the club head 1 is too large, on the otherhand, it becomes difficult to swing the golf club through the ball, andthere is a possibility that the directional stability of the struck ballis deteriorated and the carry distance is decreased. In this light, themass of the club head is preferably not less than 180 g, more preferablynot less than 185 g, but preferably not more than 210 g, more preferablynot more than 205 g.

In the case that the club head is provided with a relatively largevolume of more than 430 cc and the area of the club face 2 is relativelylarge as a necessary consequence, when the ball hitting position is offthe sweet spot towards the heel or toe, there is possibility that thedistance in the heel-and-toe direction between the hitting position andthe sweet spot becomes very large. Even in such a condition, in orderthat the rotational movement (head movement) of the club head 1 aroundthe vertical axis A1 is surely reduces to thereby stabilize thedirection of the struck ball, the lateral moment of inertia Ma should belarge enough.

Therefore, the lateral moment of inertia Ma has to be increased up to5000 g sq·cm at least. Preferably, the lateral moment of inertia Ma isnot less than 5300 g sq·cm, more preferably not less than 5500 g sq·cm.However, if the lateral moment of inertia Ma is too large, there is apossibility that the club head weight becomes excessively heavy, and theshape of the club head becomes extraordinary. Therefore, the lateralmoment of inertia Ma is at most 5900 g sq·cm.

The present inventor discovered that the club head thickness H and thevertical moment of inertia Mb have a certain correlation and that thevertical moment of inertia Mb can be kept at small values by reducingthe club head thickness H.

According thereto, by limiting the club head thickness H within a rangeof not more than 58 mm, preferably not more than 56 mm, more preferablynot more than 55 mm, still more preferably not more than 55 mm, theincrease in the vertical moment of inertia Mb can be restrained evenwhen the head volume is increased up to 430 cc at least and also thelateral moment of inertia Ma is increased up to 5000 g sq·cm at least.

If the club head thickness H is too small, the sweet spot area becomesnarrow, and as a result, the carry distances are liable to decrease.Therefore, the club head thickness H is preferably set in a range offrom not less than 45 mm, more preferably not less than 47 mm, stillmore preferably not less than 49 mm.

In order to improve the carry distance stably, the vertical moment ofinertia Mb is preferably set in a range of not more than 5000 g sq·cm,more preferably not more than 4500 g sq·cm, still more preferably notmore than 4000 g sq·cm.

If the vertical moment of inertia Mb becomes excessively small, on theother hand, there is a tendency that the head movement at impactincreases, and the carry distance is decreased, therefore, the verticalmoment of inertia Mb is preferably not less than 2500 g sq·cm, morepreferably not less than 2700 g sq·cm, still more preferably not lessthan 3000 g sq·cm.

In the case of a golf club head having a large head volume and a smallclub head thickness H, there is a tendency that the center of gravity Gof the head comes far away from the club shaft center line CL, namely,as shown in FIG. 4, the distance K tends to increase.

Accordingly, during swing, due to the centrifugal force, the club head 1is subjected to a rotational movement as indicated in broken line suchthat the center of gravity G approaches the extension of the club shaftcenter line CL when viewed from the heel side of the head.

Such rotational movement is increased in proportion to the increase inthe head speed during swing and as a result, the dynamic loft angle atimpact is increased.

In other words, the loft angle is varied depending on the swing speed,thus, it is difficult for the user to control the ballistic course andcarry distance of the ball.

In order to solve this problem, the club head 1 in this example has astreamline shape, and the crown surface length LC is set to be longerthan the sole surface length LS.

As shown in FIG. 3, at least in the vertical plane VP3 including thecenter of gravity G and the sweet spot SS, the contour of the crownportion 4 and the contour of the sole portion 5 are each defined by asmoothly curved arc line, and they are extended continuously from theedge (2 a, 2 b) of the face portion to the rearmost point BP andconnected with each other at the point BP without the side portion 6therebetween. In this vertical plane VP3, the crown surface length LC isdefined as the length measured along the outer surface of the crownportion 4 from the upper edge 2 a of the club face 2 to the rearmostpoint BP, and

the sole surface length LS is defined as the length measured along theouter surface of the sole portion 5 from the lower edge 2 b of the clubface 2 to the rearmost point BP.

Thus, at least at the rearmost point BP, the side portion 6 isinterrupted, and the head has a streamline shape.

Accordingly, during swing, the velocity of air flow along the surface ofthe crown portion becomes faster than the velocity of air flow along thesurface of the sole portion, and the air pressure to the crown portionbecomes lower than the air pressure to the sole portion, and the clubhead 1, in particular its rear part, obtains lift. Therefore, theabove-mentioned rotational movement of the head is reduced, and theresultant increase of the loft angle can be avoided, and thereby thecarry distances become stable.

If the ratio (LC/LS) of the crown surface length LC to the sole surfacelength LS is less than 1.02, the lifting is still insufficient. But, ifthe ratio (LC/LS) is more than 1.20, there is a tendency that thelifting and the restraint of the increase in the loft angle becomeexcess. Therefore, the ratio (LC/LS) is preferably not less than 1.02,more preferably not less than 1.05, but preferably not more than 1.20,more preferably not more than 1.10, still more preferably not more than1.09.

The crown surface length LC is preferably not less than 105 mm, morepreferably not less than 108 mm, still more preferably not less than 110mm, but not more than 125 mm, more preferably not more than 122 mm,still more preferably not more than 120 mm.

The sole surface length LS preferably not less than 100 mm, morepreferably not less than 103 mm, still more preferably not less than 105mm, but not more than 120 mm, more preferably not more than 117 mm,still more preferably not more than 115 mm.

Incidentally, the ratio (LC/LS) can be changed for example by settingthe radius of curvature of the contour of the crown portion 4 at smallervalues than that of the sole portion 5 and by decreasing the height BHof the rearmost point BP.

To decrease the height BH is preferable because the height of the centerof gravity G is also decreased thereby. In this light, the height BH ispreferably not more than 30 mm, more preferably not more than 28 mm,still more preferably not more than 25 mm.

If the sweet spot height GH is too large, the backspin tends to increaseexcessively. If the sweet spot height GH is too small contrary, thebackspin is decreased which tends to result in a drop ball. In eithercase, the carry distance is decreased. Therefore, the sweet spot heightGH is preferably set in a range of not more than 38 mm, more preferablynot more than 36 mm, still more preferably not more than 34 mm, but notless than 25 mm, more preferably not less than 27 mm, still morepreferably not less than 29 mm.

The face progression FP has influence upon the returning motion of theclub head from swing and upon the timing of impacting the ball. Bysetting the face progression FP in a range of not less than 17 mm,preferably not less than 19 mm, but not more than 28 mm, preferably notmore than 26 mm, more preferably not more than 25 mm, the directionalstability of the struck ball can be improved to stabilize the carrydistance.

If the gravity point depth GL is decreased, there is a possibility thatthe lateral moment of inertia Ma becomes decreased, therefore, thegravity point depth GL is preferably not less than 30 mm, morepreferably not less than 32 mm, still more preferably not less than 33mm. If the depth GL is too large, on the other hand, the head tends tobecome insensitive to the impact feeling. Further, the position of thesweet spot SS tends to become high, and potential for off-center hit(lower hit) increases. It is therefore preferable that the gravity pointdepth GL is set to be not more than 60 mm, more preferably not more than57 mm, still more preferably not more than 55 mm.

In order to secure the lateral moment of inertia Ma and the gravitypoint depth GL, the size HL of the club head 1 measured in theback-and-forth direction from the leading edge Le to the rearmost pointBP, is preferably set in a range of not less than 110 mm, morepreferably not less than 115 mm, but not more than 127 mm, morepreferably not more than 125 mm.

Although the club head 1 is decreased in the club head thickness H andthe vertical moment of inertia Mb as explained above, the vertical geareffect occurs more or less.

In this embodiment, the face roll is provided throughout the club face 2and the radius of curvature PR is set in a range of not less than 12inches, preferably not less than 14 inches, more preferably not lessthan 16 inches, but not more than 25 inches, preferably not more than 23inches, more preferably not more than 21 inches. These specific valuesof the radius of curvature RR are measured in the above-mentionedvertical plane VP3 for the part between a point Pu 10 mm downward fromthe upper edge 2 a along the club face 2 and a point Pd 10 mm upwardfrom the lower edge 2 b along the club face 2, as shown in FIG. 3.

In this embodiment, because of the relatively large lateral moment ofinertia Ma, even if the ball hitting position is off the sweet spottowards the toe or heel, the sidespin of the struck ball is not soincreased. Therefore, it is preferable that the radius of curvature RBof the face bulge is increased. Preferably, the radius of curvature RBis set in a range of not less than 15 inches, more preferably not lessthan 17 inches, still more preferably not less than 20 inches, but notmore than 50 inches, more preferably not more than 45 inches, still morepreferably not more than 40 inches.

In the plan view of the club head under the standard state, the overallarea of the club head is preferably set in a range of not less than 115sq·cm, more preferably not less than 117 sq·cm, still more preferablynot less than 120 sq·cm. In other words, the projected area of the headon the horizontal plane HP is so limited. As a result, the lateralmoment of inertia Ma can be effectively increased, and it is possible togive the user easy fillings when addressing the ball. If the projectedarea is too large, on the other hand, violation of the golf rules orregulations and an undesirable increase in the club head weight areresulted, therefore, the projected area is preferably not more than 140sq·cm, more preferably not more than 137 sq·cm, still more preferablynot more than 135 sq·cm.

Comparison Tests

Wood-type hollow golf club heads were prepared and tested for the carrydistance and the directional stability of the struck ball. All of theclub heads had same structures and same specifications except for thespecifications shown in Table 1. The volume, mass, lie angle and loftangle of the heads were 460 cc, 195 grams, 59 degrees and 11.5 degrees,respectively. The heads were each made from a main part formed bycasting a molten titanium alloy Ti-6Al-4V, a face plate formed byforging a titanium alloy Ti-5.5Al-1Fe, and a crown plate formed byforging a titanium alloy Ti-15V-3Cr-3Al-3sn.

The main part was provided with a front opening and a top opening. Theface plate and crown plate were laser welded to the main part so as tocover the front opening and the top opening, respectively.

The moments of inertia Ma and Mb were adjusted by changing the wallthicknesses of the sole portion, side portion and/or crown portion.

Carry Distance Test:

Each head was attached to an FRP shaft (MP400, flex R, manufactured bySRI Sports Limited) to make a wood club.

The club was mounted on a swing robot and hit three-piece balls fivetimes par each of the following three positions at a head speed of 40m/s.

Center: the sweet spot sS

upper: 5 mm above the sweet spot

Lower: 5 mm below the sweet spot

with respect to each of the three positions, the average carry distancewas calculated. Further, the average of all of the positions wascalculated. The results are shown in Table 1.

Variation in Carry Distance Test:

Using the above-mentioned golf clubs, each of ten golfers havinghandicaps of 10 to 20 hit three-piece balls ten times par a club.

With respect to each of the golfers, the difference between the maximumcarry distance and minimum carry distance was obtained. Then, theaverage of the differences of the ten golfers was calculated. Theresults are shown in Table 1, wherein the smaller the value, the smallerthe variation.

TABLE 1 Head Ex. 1 Ex. 2 Ex. 3 Ref. 1 Ex. 4 Ex. 5 Ex. 6 Club headthickness H (mm) 45.0 50.0 55.0 60.0 55.0 55.0 55.0 Lateral moment ofinertia Ma (g sq · cm) 5850.0 5640.0 5450.0 5070.0 5370.0 5350.0 5475.0Vertical moment of inertia Mb (g sq · cm) 3200 3350 3480 3360 3370 34003450 Crown surface length Lc (mm) 113.0 115.0 118.0 120.0 110.0 114.0120.0 Sole surface length Ls (mm) 108.0 110.0 112.0 114.0 114.0 112.0110.0 Ratio (Lc/Ls) 1.05 1.05 1.05 1.05 0.96 1.02 1.09 Sweet spot heightGH (mm) 28.2 30.0 32.5 37.5 36.7 34.0 33.0 Gravity point depth GL (mm)50.2 46.3 44.8 43.1 43.5 44 44.5 Face roll radius PR (inch) 17 17 17 1717 17 17 Face bulge radius RB (inch) 20 20 20 20 20 20 20 Club headprojected area (sq · mm) 127 127 127 127 127 127 127 Average carrydistance (yard) Upper 218.3 217.9 216.3 213.5 214.2 215.6 216.1 Center225.4 225.1 224.7 224.5 224.7 224.6 224.7 Lower 217 215.1 213.5 210.2212.4 212.9 213.4 All 220.2 219.4 218.2 216.1 217.1 217.7 218.1Variation of Carry distance (yard) 10.8 11.2 11.7 12.5 16.7 12.8 9.5

From the test results, it was confirmed that the decrease in the carrydistance at the time of upward or downward off-center shot can besignificantly controlled, and the stable carry distances can beachieved.

1. A hollow golf club head having a head volume of not less than 430 cc,a lateral moment of inertia of from 5000 to 5900 g sq·cm, and a clubhead thickness of from 45 to 58 mm.
 2. The head according to claim 1,wherein in a vertical plane including a sweet spot and the center ofgravity of the head, a crown surface length measured along the upperouter surface of the club head from an upper edge of a club face to therearmost point of the club head is more than a sole surface lengthmeasured along the lower outer surface of the club head from a loweredge of the club face to the rearmost point of the club head.
 3. Thehead according to claim 1, wherein in a vertical plane including a sweetspot and the center of gravity of the head, a crown surface lengthmeasured along the upper outer surface of the club head from an upperedge of a club face to the rearmost point of the club head is in a rangeof from 1.02 to 1.20 times a sole surface length measured along thelower outer surface of the club head from a lower edge of the club faceto the rearmost point of the club head.